The present invention relates to solar cells and more particularly to solar cells which provide increased absorption of solar radiation.
A major problem in the field of solar energy collection is the maximization of collection of weakly absorbed solar radiation. Solar radiation comprises radiation of both short and long wavelengths. The absorption coefficient of a semiconductor material depends on the forbidden bandgap widths of the particular semiconductor material. Usually for the semiconductor materials, used in the active region of a solar cell, absorption of the larger wavelength portion of the solar spectrum will be weaker than the short wavelength portion. To adjust for this weak absorption of long wavelength solar radiation it was necessary to make the semiconductor material sufficiently thick to assure absorption. Of course, increasing the thickness of the semiconductor material used in the solar cell increases the cost.
Another problem encountered in solar cells is having electrical contacts on the solar cell which do not interfere with solar radiation incident onto the cell. Solar radiation falling onto a contact will probably be reflected away from the cell, lowering the solar cell's collection efficiency. While it is important to prevent the loss of solar radiation collection, it is also important to have electrical contacts on the solar cell which are conveniently located for the current generated anywhere in the cells' active region. If an electrical contact is only around the periphery of a solar cell it will not interfere with solar radiation incident onto the cell, but current generated within the solar cell will have to travel a greater distance to the contact than current generated at the cells' periphery. The farther current must travel through the semiconductor material to the contact, the larger the resistance it will encounter, and thus the lower the power conversion efficiency.
Therefore, it would be most desirable in the field of solar cells to provide (1) maximization of solar radiation collection without the cost of thick active regions, and (2) electrical contacts not interfering with incident solar radiation but yet are conveniently located to current generated anywhere in the active region.